1. Field of the Invention
The present invention relates to a lens barrel for use in cameras such as 35 mm single lens reflex (SLR) cameras, motion picture cameras and TV cameras, and more particularly to a lens barrel capable of being automatically and manually controlled to adjust the focus.
2. Description of Prior Art
In a prior art Japanese Patent Application laid open under No. 50-151144, it is known to engage an attachment, which is driven by an automatic focus control device, with the focus control ring of a lens barrel. In the case of automatic focus control, the attachment is engaged with the focus control ring for rotating it by the automatic focus control device. The attachment is disengaged from the focus control ring for allowing a free rotation thereof for manual focus control. Thus, the focus control can be achieved alternatively by manual control means or automatic control means.
In the above mentioned prior art, however, the automatic focus control device is inevitably provided with considerable power in order to drive the attachment since the focus control ring of a lens barrel usually has an adequate resistance to prevent an undesirable easy rotation thereof. Further, the use of such a prior art focus control device results in an inconvenience for manual focus control operation, as well as bulkiness, and unshapeliness of the camera since the attachment is to be engaged with the lens barrel on the outside thereof at the focus control ring.
In addition, U.S. Pat. No. 3,798,660 discloses a lens mount of an SLR camera that is shifted along the optical axis by the power of the automatic focus control device to shift the whole exchangeable lens barrel attached to the lens mount. In such a system, however, a rigid mechanism is required for the shiftable lens mount to support the weight of the whole lens barrel, as well as sufficiently great power for the automatic focus control device to drive the whole lens barrel.